1. Field of the Invention
The present invention generally relates to an antenna structure, and more particularly, to a planar antenna structure built in an electronic device.
2. Description of Related Art
In keeping pace with progress in telecommunication technology, application of the telecommunication technology for hi-tech products has been increasing and related telecommunication products have become diversified. In recent years, the consumer functional requirements for telecommunication products have become increasingly higher; therefore, telecommunication products with various designs and functions are continuously brought to market, and the computer network products with wireless networks are in demand.
Since antenna design affects the communication quality of communication products, it is the key factor of communication products. Generally, antennas comprise internal antennas and external antennas. External antennas comprise monopole antennas, dipole antennas and helix antennas. Internal antennas comprise planar inverted F antennas (PIFA) and microstrip antennas. The PIFA is widely used in communication products.
FIG. 1 is a three-dimensional diagram showing a conventional PIFA. FIG. 2 is a side view showing the conventional PIFA as shown in FIG. 1. Please refer to FIGS. 1 and 2, the conventional PIFA 100 comprises a ground conductor 110, a radiating patch 120, a shorting patch 130 and a feeding patch 140. The radiating patch 120 is disposed above the ground conductor 110, and the ground conductor 110 is parallel with the radiating patch 120 with a suitable distance, and the radiating patch 120 has a feed point FP. In addition, one end of the shorting patch 130 is connected to the ground conductor 110, and the other end of the shorting patch 130 is connected to one side of the radiating patch 120. Further, one end of the feeding patch 140 is connected to the FP on the radiating patch 120, and the other end is electrically connected to a signal source SS.
For achieving the performance of dual-frequency antenna, a groove 124 may be additionally formed on the radiating patch 120 of the PIFA 100 in order to divide the radiating patch 120 into an outer first radiating part 120a and an inner second radiating parch 120b. The first radiating part 120a and the second radiating part 120b may serve as a first radiator of a first frequency band and a second radiator of a second frequency band, respectively, for operating in two different operation frequencies.
FIG. 3 is a radiation pattern of the PIFA shown in FIG. 1 at 2.45 GHz during operation; FIG. 4 is a radiation pattern of the PIFA shown in FIG. 1 at 5.25 GHz during operation. From FIGS. 3 and 4, the beam width of the conventional PIFA is narrower. It means that the signal receiving/transmitting area of the PIFA is limited to a smaller region above the radiating patch. Accordingly, how to increase the signal receiving/transmitting area of the PIFA is an important issue.